Contour of Electrically Induced Premature Ventricular Beats Before and After Experimental Myocardial Infarction in Dog

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Abstract
Ventricular premature beats were produced by stimulating electrodes inserted into the anterolateral right ventricular and into the midlateral left ventricular wall of 13 openchest anesthetized dogs. In 9 of the 13, acute myocardial infarction deformed the final deflection of the experimentally induced ventricular extrasystoles so that they mimicked the diagnostic pattern present in the beats of sinus origin. In 4 of the 13, no changes occurred in either the extrasystoles or in the beats of sinus origin until the infarcted region was brought into contact with the thoracic wall, at which time diagnostic patterns of infarction appeared in both types of ventricular complexes. Reinfarction produced by ligating an additional coronary branch produced comparable changes in the final deflection of the premature and sinus-propagated beat. These findings suggest that the inscription of the terminal deflections of premature ventricular beats is dominated by events within the infarcted region. They support the clinical concept that the configuration of ventricular extrasystoles may be of value in the recognition of acute myocardial infarction. The findings do not explain, however, the occasional absence of diagnostic findings in ventricular premature beats in electrocardiograms otherwise diagnostic of human myocardial infarction.